The invention relates to steam turbines and, more particularly, to a steam turbine utilizing IP extraction flow for inner shell cooling.
Steam turbines are often used for large power systems having a steam turbine and a steam generating source. The source may come in the form of single or multiple gas turbines coupled with single or multiple heat recovery steam generators or a coal fired boiler or a nuclear reactor. The steam turbine and source(s) drive an electrical generator as the load. Many arrangements for steam turbines in a power plant have been proposed. In a steam turbine thermal cycle, the hot exhaust gas from a combustion gas turbine or coal combustion in a boiler or fission reaction in a nuclear reactor contributes heat energy to partially or wholly generate the steam used in the steam turbine.
A steam turbine is a mechanical device that extracts energy from pressurized steam and converts the energy into work. Steam turbines receive a steam flow at an inlet pressure through multiple stationary nozzles that direct the steam flow against buckets rotationally attached to a rotor of the turbine. The steam flow impinging on the buckets creates a torque that causes the rotor of the turbine to rotate, thereby creating a useful source of power for turning an electrical generator or the like. The steam turbine includes, along the length of the rotor, multiple pairs of nozzles (or fixed blades) and buckets. Each pair of nozzle and bucket is called a stage. Each stage extracts a certain amount of energy from the steam flow causing the steam pressure to drop and the specific volume of the steam flow to expand.
Generally, a steam turbine has multiple extractions from its steam path. Extractions are used in feedwater heaters to improve the cycle heat rate. With reference to FIG. 1, typically, the extraction from IP exhaust 12 is provided to a feedwater heater 14. It would be desirable to recover the waste heat from the inner shell to thereby improve steam turbine performance.